In order to correctly demodulate a wireless signal received by a receiving device in a wireless communication system, it is generally necessary to perform synchronization of the frequency and time (symbol timing, frame timing, etc.) of a received wireless signal. If the received wireless signal undergoes some interference, a technique for demodulating the reception signal including an interference component is required. Examples of receiving techniques which are effectively used when a plurality of wireless reception signals, which are reception targets, having the same signal format overlaps on a time or frequency axis to cause interference, include a method (first technique) of performing interference cancellation typified by successive interference cancellation (SIC) used for bell laboratory layered space-time (BLAST) or the like in multiple input multiple output (MIMO) and a method (second technique) of performing maximum likelihood estimation on all overlapping signals.
The first technique and the second technique are kinds of synchronous detection methods applicable when the frequency and time of transmitted wireless signals are obtained with some synchronization method. The first technique requires frequency and time information for generating a replica from a demodulation result even when differential transmission signals are demodulated using asynchronous detection.
A synchronization technique for Gaussian-filtered frequency shift keying (GFSK) or Gaussian-filtered minimum shift keying (GMSK) signals is disclosed as a technique for estimating the frequency and time of a wireless reception signal when interference occurs (Patent Literature 1). However, Patent Literature 1 does not disclose a method of estimating the time and frequency of each of a plurality of wireless reception signals when the plurality of wireless reception signals interferes with each other. For example, in a case where a receiving device that is mounted on a moving vehicle, an aircraft, a satellite, or the like (hereinafter collectively referred to as a moving object) receives signals transmitted from a plurality of transmitting devices that shares a frequency band with each other but having time axial shifts or frequency axial shifts that are not necessarily the same, a plurality of transmission signals interferes with each other, and it is necessary to estimate the time and frequency of each transmission signal in order to receive the interfered signals. Examples of methods that can be used in such a case include: a method of performing correlation processing by using a synchronization signal such as a preamble and adding time and frequency shifts to the synchronization signal, and obtaining the time and frequency at which a peak is given as an estimation result; and a method of using a sparse coding technique such as orthogonal matching pursuit (OMP) to obtain time, frequency, and payload information as bases, and selecting some bases from a dictionary which is a set of them to obtain a time and frequency estimation result.